Radio communication systems utilizing multiplexed noise codes are generally known. A typical example is shown and described in U.S. Pat. No. 4,293,953, entitled, "Bi-Orthogonal PCM Communications System Employing Multiplexed Noise Codes", which issued to Frank S. Gutleber, the present inventor, on Oct. 6, 1981.
The concept of code expansion for the general class of multiplexed noise codes comprised of code mate pairs having autocorrelation functions which upon detection provide an impulse function is also generally known. One known expansion concept involves the butting of one code mate with the other code mate and is a technique disclosed, for example, in U.S. Pat. No. 3,461,451, entitled, "Code Generator to Produce Permutations of Code Mates", which issued to the present inventor on Aug. 12, 1969. Additionally, the concept of partially overlapping code mate pairs to form expanded code mates is shown and described in the above cross referenced related application, U.S. Ser. No. 497,956, entitled, "Noise Code Generator And Pulse Compression Communications System Therefor", now U.S. Pat. No. 4,455,662 while the concept of generating one type of interleaved code mate pairs is shown and described in the above cross referenced related application, U.S. Ser. No. 499,727, entitled, "Code Generator For Interleaved Multiplexed Noise Codes".
Accordingly, it is an object of the present invention to provide an improvement in the generation and utilization of multiplexed noise codes.
Another object of the invention is to provide an expansion of multiplexed noise code mate pairs by partially interleaving the code bits of code mate pairs
Still a further object of the invention is to provide an expansion of multiplexed noise code mate pairs into partially interleaved code mate pairs having autocorrelation functions which upon detection with a matched filter provides an impulse autocorrelation function.
These and other objects are achieved by a method and apparatus for generating and utilizing a pair of expanded multiplexed noise codes from multi-bit code mate pairs having code bits of equal pulse width (2.tau.) by first reducing the pulse width of each of the original code bits of both code mates by one half to form a pair of intermediate code mates having code bits of pulse width (.tau.), then delaying one of the intermediate codes by a least three times the pulse width of the intermediate code bits, i.e., 3.tau. and adding it to the other intermediate code mate to form a first partially interleaved code mate, while a second partially interleaved code mate is generated by subtracting the delayed intermediate code mate from the other intermediate code mate and effected, for example, by forming the negative of the delayed intermediate code mate and adding it to the other intermediate code mate. The resulting partially interleaved code mates compress to an impulse when they are detected with their respective matched filters and linearly added.